To comply with statutory emission limiting values, modern diesel vehicles are equipped with a high-pressure exhaust gas recirculation, abbreviated HP-EGR, i.e., exhaust gas is diverted upstream from the exhaust gas turbocharger turbine and fed back to the fresh air end downstream from the exhaust gas turbocharger compressor, and a low-pressure exhaust gas recirculation, abbreviated LP-EGR, i.e., exhaust gas is diverted downstream from the particle filter and fed back into the fresh air end immediately downstream from the air flow meter. Legislation in a few markets, such as the United States, for example, requires monitoring of HP- and LP-EGR as well as, in the event of a defect, identification of the actually defective EGR path, i.e., HP- or LP-EGR. The diagnostic methods detect a defect in the exhaust gas recirculation system but cannot always assign it definitively to the high-pressure path or the low-pressure path since this would require operating points at which only the high-pressure exhaust gas recirculation path is active or only the low-pressure exhaust gas recirculation path is active.
German patent document DE 11 2008 002 195 T5 discusses a method and a device for monitoring an intake air compressor device having a variable geometry. In the method described there, an exhaust gas pressure and a guide vane position of the turbocharger device having a variable geometry are monitored. The exhaust gas pressure and the guide vane position are estimated. A residual value for the exhaust gas pressure and a residual value for the guide vane position are calculated on the basis of differences between the estimated and monitored exhaust gas pressures and guide vane positions.
On the basis of the residual value for the exhaust gas pressure and the residual value for the guide vane position, it is determined that the turbocharger is functioning properly.
German patent document DE 11 2007 001 467 T5 discusses a method for simultaneous exhaust gas recirculation and control of the combustion phase angle of a motor vehicle, combustion phase angle information being supplied by the cylinder pressure detection device, and the fuel supply device being regulated according to setpoint values and feedback in the combustion phase angle information. Furthermore, with the method described there, the exhaust gas recirculation device is regulated according to setpoint values and feedback in the case of a preselected exhaust gas recirculation control parameter. The setpoint values in the preselected exhaust gas recirculation control parameters are set on the basis of a comparison of the settings on the fuel supply device.